The preparation of ethers, including unsymetrical ethers, by reaction of an olefin with a glycol is well known in the art. The resultant reaction mixture, containing desired glycol ether product, undesired by-products, and unreacted reactants such as glycol, are normally separated in conventional manner by distillation, following removal of catalyst or condensing agent, if employed. In the case of production of 1-t-butoxy-2-propanol, isobutylene is reacted with an excess quantity of propylene glycol in the presence of a solid resin etherification catalyst at appropriate reaction temperatures and pressure to produce a crude reaction product comprised of desired 1-t-butoxy-2-propanol (PTB-1), by-product 2-t-butoxy-1-propanol (PTB-2) unreacted isobutylene and propylene glycol, as well as minor amounts of tertiary butyl alcohol and water. The hydroxyl groups of the glycol ether products produced further react with isobutylene to form the di-ether, 1,2-di(t-butoxy) propane, (DPTB), which is an undesirable by-product. The vapor liquid equilibrium data of the reaction mixture show the following ratio of relative volatilities at 178 mm pressure: EQU PTB-1/PTB-2=1.38 EQU PTB-1/DPTB=1.54 EQU PTB-2/DPTB=1.12
However in the actual batch distillation data, it appeared that 1,2-di(t-butoxy) propane was lighter than indicated by the ratio of relative volatilities.
Accordingly, it has been found to be difficult to recover 1-t-butoxy-2-propanol from crude etherification reaction products which exhibit sufficiently low 1,2-di(t-butoxy) propane content to permit commercial use of the desired propylene glycol monotertiary butyl ether in commercial applications, such as in coatings, cleaners, electronic chemicals and inks.
Hence, it is an object of the present invention to provide a process for recovering 1-t-butoxy-2-propanol in a high state of purity without substantial loss while containing minimal amounts of 2-t-butoxy-1-propanol and especially of undesired 1,2-di(t-butoxy) propane from the reaction product obtained by reaction of isobutylene with propylene glycol. Other objects will become apparent to those skilled in the art from the following description.